1. Field of the Invention
This invention relates to electric power supplies and more particularly relates to high efficiency redundant electric power supplies.
2. Description of the Related Art
A power supply, sometimes known as a power supply unit or PSU, is a device or system that supplies electric power to an output load or group of loads. A power supply may be configured to convert power from one form to another form, such as converting AC electric power to regulated DC electric power. The regulation of power supplies is typically done by incorporating circuitry to tightly control the output voltage and/or current of the power supply to a specific value. The specific value is closely maintained despite variations in the load presented to the power supply's output, or any reasonable voltage variation at the power supply's input.
For example, in an electric device such as a computer, the power supply is typically designed to convert an AC voltage input such as is traditionally provided by a conventional wall socket, into several low-voltage DC power outputs for transmission to the internal electric components of the computer. Conversion is typically performed in stages that may include different stages such as a rectification stage, an active filter stage, a regulator stage, etc. The various stages may be a boost, a buck, or other derivative topology. In one embodiment of a conventional power supply, a regulator stage may be implemented to provide a number of different voltages to a computer system via a bus. For example, the power supply may include a regulator stage that regulates voltages on the bus of +12 volts, +5 volts, +3.3 volts, and −12 volts. These regulated voltages are then provided to the computer system which uses the different voltages to power the various electrical sub-systems of the computer system.
For high availability systems, it is often desirable that a single failure will not cause the system to be unavailable. One solution is to provide redundant power by using two or more separate power supplies. This solution has an advantage of being very reliable, since if any one power supply fails, the other can pick up the load of the failed power supply. Two or more power buses are often used as an additional layer of redundancy in case of a power bus fault. Each power bus is usually connected to each of the power supplies using ORing metal-oxide-semiconductor field-effect transistors (“MOSFETs”). The ORing MOSFETs can isolate power supplies and power buses from the electric load in fault situations, allowing continued availability of the system.
Because an ORing MOSFET is often used at each power bus connection at both the inputs and outputs of the power buses, the number of MOSFETs used in the system increases the cost of the system, and reduces the system's energy efficiency. For example, some MOSFETs cost about $4 each. A system with four power supplies and two power buses may have ten MOSFETs, adding about $40 to the cost of the system. A power supply system that eliminates the use of some of the ORing MOSFETs without reducing redundancy or fault protection would decrease the cost of the system significantly and increase energy efficiency by several percent.
FIG. 1 is an example of a traditional system 100 for providing reliable power. The system 100 includes two AC power sources 102, 104, four power supplies 110, 112, 114, 116, two buses 118, 120, and a load 122. Each power supply 110, 112, 114, 116 is connected to each of the two buses using switches Q1-Q8. Each bus 118, 120 connects to the load 122 through a switch Q9, Q10. The system 100 is very flexible, but also requires a lot of switches and connections which brings raises the cost of the system.